1. Field of the Invention
The present invention pertains to a device for sensing the engagement of a pickup head having gripping means with stacked workpieces in sheet form, such as fabric, plastic, paper and the like.
With such a device, it is possible to detect failure of a pickup head to engage a workpiece, resulting in activation of a warning signal that indicates that workpieces are not being removed from the stack. Such a signal can be timed to initiate the cessation of operation of the pickup head, which is first caused to be lowered to engage and grip a workpiece, then raised to remove the workpiece from the stack and thence rotated so the workpiece can be released to be deposited in a predetermined location.
2. Description of the Prior Art
A device for picking up workpieces by means of one or more pickup heads having fixed and movable teeth that are caused to penetrate the thickness of a workpiece to be removed are shown and described in U.S. patent application No. 377,285, filed on May 12, 1982 by the applicant of this application, and assigned to the assignee of the present invention. Additionally, these types of pickup heads can be provided with gripping elements that define adhesive members attached to the underside of the pickup heads.
The known devices for separate and individual removal of workpieces from a stack perform their intended functions quite satisfactorily on many types of workpieces; however, they are considered to have certain disadvantages by not being able to detect failure of the device to engage and grip a workpiece, which can be attributed to the type of material from which it is made, or by a malfunction of the gripping means. In either case, conditions of this nature are not immediately detected by the operator who otherwise would be able to intervene and correct such conditions.
The device comprising the invention provides a means for overcoming the disadvantages of known devices by a sensing apparatus which immediately detects and warns the operator when the device fails to remove a workpiece from the stack.